Objective

This study analyzed attentional performance in patients with schizophrenia during a continuous performance task requiring a high response rate.

Method

The Conners’ Continuous Performance Test-II (CPT-II) was administered to 64 patients with schizophrenia and 64 healthy comparison subjects. A cross-sectional design was used in order to allow analysis of the means between patients and healthy subjects. Differences in performance were assessed for significance using ANCOVA. Percentiles were also analyzed in order to determine whether a participant showed normal or pathological performance. Pearson's correlation was used to detect possible relationships between attentional performance and psychopathology.

Results

Of the 12 CPT-II measures, response style and slowing of reaction time (RT) between targets increased to similar extents between patients and healthy comparison subjects. Patients performed significantly less well than non-patient group on all other measures. Nevertheless, patient's performance on four of these measures remained within the normal range, and patient's performance on the remaining measures qualified as pathological only in the case of variability in hit RT. No significant correlations between attention performance and symptoms were found.

Conclusions

These results suggest that although patients may show lower attentional functioning than non-patients on tasks requiring a high response rate, their attentional performance remains within the normal range on most dimensions.

Introduction

Schizophrenia is recognized as a neurobiological disorder with a strong neurocognitive component (Harrison & Weinberger, 2005; Keshavan, Tandon, Boutros & Nasrallah, 2008). The profile of these neurocognitive deficits includes deficits in attention, processing speed, working memory, learning, and executive function (Barch, 2005; Kalkstein, Hurford & Gur, 2010). Attention deficits have been the focus of extensive research because they are one of the main complaints of schizophrenic patients in their daily life (Ikebuchi, Nakagome & Takahashi, 1999) and are also markers of vulnerability for the disease (Nuechterlein, Dawson & Green, 1994). Furthermore, an adequate attentional functioning may be an important prerequisite for higher cognitive functions (Oberauer, 2002).

One of the most widely used instruments for assessing attention is the Continuous Performance Test (CPT). Most studies involving CPTs follow the same basic paradigm established by Rosvold, Mirsky, Sarason, Bransome and Beck (1956): a series of stimuli are presented (e.g. letters), and the subject must press a key when a specified stimulus appears (e.g. the letter X). Most studies of CPT in patients with schizophrenia have reported a performance deficit with respect to non-patients (Cornblatt, Obuchowski, Schnur & O'Brien, 1997; Heinrichs & Zakzanis, 1998; Rapisarda et al., 2014; Riccio, Reynolds & Lowe, 2001). This deficit is observed not only during acute episodes of the disease but also during periods of remission (Liu et al., 2006). A similar deficit has been reported in first-degree relatives of individuals with schizophrenia (Snitz, MacDonald & Carter, 2006), as well as in individuals exhibiting characteristics of schizotypic personality disorder (Keefe et al., 2006). Thus, this deficit has been proposed as a marker of vulnerability to schizophrenia (Hazlett, Dawson, Schell & Nuechterlein, 2008; Pukrop et al., 2007; Yung et al., 2007). Cornblatt and Malhotra (2001) conclude that deficits in verbal and spatial attentional processing tapped by the CPT-Identical Pairs (CPT-IP) are heritable, developmentally stable, independent of clinical state, and predict future spectrum disorders in the at-risk offspring of parents with schizophrenia. In addition, various studies have shown that the magnitude of the performance deficit increases with increasing CPT difficulty (Kumar et al., 2010; Kurtz, Ragland, Bilker, Gur & Gur, 2001; Lee et al., 2012; Mass, 2002; Vázquez, Nieto-Moreno, Cerviño & Fuentenebro, 2006). In fact, recent work from the Consortium on the Genetics of Schizophrenia found the CPT-IP (Cornblatt, Lenzenweger & Erlenmeyer-Kimling, 1989), which places greater demand on working memory (the target is not a fixed number but rather requires temporarily storing each stimulus, comparing it with the next, and then match the prior one), to be more sensitive at detecting the performance deficit between patients and healthy controls than the Degraded Stimulus CPT (CPT-DS), which places greater demand on perceptual processes by blurring visual stimuli (Nuechterlein et al., 2015).

Although CPTs have traditionally been used as indicators of sustained attention (Ballard, 1996; Mirsky, Anthony, Duncan, Ahearn & Kellam, 1991), they probably also measure other components of attention (Riccio et al., 2001), with different mechanisms of attentional deficit giving rise to different patterns of performance on CPTs. This may be particularly important for analyzing patients with schizophrenia, who may show a range of alterations in attentional subfunctions (Egeland & Kovalik-Gran, 2010; Egeland, 2007; Rund et al., 2006), which likely reflect diverse neurological alterations, both structural and functional (Ren et al., 2013). All CPTs comprise a standard array of response measures that include the rate of omission errors (when the subject fails to detect the target stimulus) and the rate of commission errors (when the subject incorrectly identifies a stimulus as the target one). Incorporating aspects of signal detection theory (Green & Swets, 1966) into the CPT allows researchers to assess additional performance measures, such as signal detectability (d’), response bias (β), and reaction time (RT). The measure d’ reflects the proportion of the signal-noise distribution that is attributable to true perception of the signal, while β is the decision criterion, indicating what proportion of the distribution is attributable to the subjective threshold set by the participants for deciding whether to respond. More recent works draws on a wider array of measures, generating more precise and comprehensive results. For example, if we assume that a fast RT indicates faster discrimination of the target stimulus, then both the RT values themselves and their variability can provide additional insights into detectability. For example, Lysaker, Tsai, Henninger, Vohs and Viverito (2010) found a significant relationship between variability of RT on a CPT and social functioning of patients with schizophrenia; in contrast, earlier studies involving fewer testing measures were unable to distinguish patients with different social functioning based on their performance on a CPT (Cohen et al., 2007; Yung, Phillips, Yuen & McGorry, 2004). In fact, some authors argue that the score of the errors is less important when CPT results are interpreted (Aaron, Joshi & Phipps, 2004), highlighting the need to consider more variables.

The standard Conners’ CPT (Conners, 2004) encompasses 12 measures that may reflect different dimensions of attention. Two characteristics of the standard CPT give it advantages over other CPTs. One characteristic is that the target stimulus appears during much of the testing, such that participants need to respond to most of the stimuli presented. This makes the tendency to respond more difficult to inhibit. For this reason, most CPTs use a lower signal–noise ratio, meaning that participants need to respond to fewer stimuli, making them more sensitive to attentional maintenance. The high signal–noise ratio of Conners’ CPT makes it more sensitive to commission errors. A high frequency of commission errors, together with a fast response style, is considered as a measure of hyperactivity–impulsivity, which is generally related to the integrity of the frontal lobes (Olsen et al., 2013; Wu, Gau, Lo & Tseng, 2014). Errors on CPTs requiring a high response rate are associated with greater likelihood of lapses in attention (Robertson, Manly, Andrade, Baddeley & Yiend, 1997) and complaints of cognitive problems in daily life (Manly, Robertson, Galloway & Hawkins, 1999), including attention-related cognitive problems (Cheyne, Carriere & Smilek, 2006). Most studies using CPTs to analyze patients with schizophrenia have applied tests with a low signal–noise ratio and have concluded that these patients do not exhibit impulsivity (Mass, 2002; Nieuwenstein, Aleman & de Haan, 2001). However, the results may be different if a test more sensitive to commission errors, such as the standard Conners’ CPT, was used. The fact that the standard Conners’ CPT requires participants not just to pay attention constantly but to respond constantly makes it more vulnerable to fatigue effects. To account for time-dependent decreases in attention during testing, researchers can examine changes in RT and RT variability between testing blocks. The second characteristic that differentiates the standard Conners’ CPT from other CPTs is that it differentiates RTs according to the duration of the previous inter-stimulus interval (ISI). This allows analysis of whether the participant's activation levels depend on the stimulus intensity. Therefore, the present study analyzed the attentional performance of individuals diagnosed with schizophrenia using a CPT requiring a high response rate, namely the standard Conners’ CPT. In addition, the study examined possible correlations between clinical characteristics of the patients and attentional performance.

Relationships between performance deficits on the CPT and schizophrenia symptomatology are thought to reflect the idea that structural and/or functional neurological alterations cause both the disorder itself and associated cognitive deficits (Lesh, Niendam, Minzenberg & Carter, 2011). Studies examining relationships between various dimensional models of symptomatology and cognitive functioning seem to concur that patients with predominantly positive symptoms, such as hallucinations and delusions, show smaller deficits in cognitive functioning (Seltzer, Conrad & Cassens, 1997), whereas those with more negative symptoms, such as lack of affect, show greater cognitive deficits (Grawe & Levander, 2001; Liddle, 2000; Penadés, Gastó, Boget, Catalán & Salamero, 2001; Villalta-Gil et al., 2006). Honey and colleagues (2003) found that deficits in frontal lobe-mediated cognitive functions are associated with negative symptomatology, whereas temporal lobe-mediated functions are associated with positive symptoms. Despite having found relationship between positive symptoms and cognitive functioning, the specific relationship between psychotic symptomatology and attention is less clear. Some studies have linked symptoms with attentional deficits (Buchanan, Strauss, Brier, Kirkpatrick & Carpenter, 1997), while others have found no such association (Addington & Addington, 1998; Nuechterlein et al., 2015). Some studies indicate the two to be at least partially independent of each other, because attentional deficits can remain even when symptoms have subsided. Other studies, in contrast, have reported associations between sustained attention and positive symptomatology (Rund et al., 2004), and between selective attention and paranoid thoughts (Fear, Sharp & Healy, 1996) as well as inhibition and hallucinations (Waters, Badcock, Michie & Maybery, 2006). Still other studies have linked inhibition, flexibility and sustained attention with negative symptomatology (Heinrichs, 2005; Voruganti, Heslegrave & Awad, 1997). These divergent and occasionally conflicting findings in the literature may reflect the different CPTs used, because more difficult CPTs can place additional processing demands on the subject. The divergent findings may also reflect the different symptom dimensions analyzed. In any event, the literature contains various models of the relationship between schizophrenia symptoms and attentional deficits (Harvey, Rabinowitz, Eerdekens & Davidson, 2005), highlighting the need for studies aimed at clarifying this relationship as well as its underlying mechanisms.

In this study, we attempted to measure the performance of patients with schizophrenia in a CPT requiring a high response rate. We expected patients to perform worse than healthy comparison subjects. We also explored the relationship of attentional performance to clinical symptomatology. We hypothesized that attentional functioning would correlate inversely with negative symptomatology.

Materials and Methods

Subjects

The sample contained outpatients diagnosed with schizophrenia at the Center for Mental Health in “Jaén (Spain)”. Patients were included in the study if they were aged between 18 and 55 years, had been diagnosed with schizophrenia according to DSM-5 criteria (American Psychiatric Association, 2013), showed stable symptomatology, did not have a history of brain damage or another psychiatric disorders, and no drug use at least in the last year or have a history of drug abuse. All participants were on antipsychotic medication during the study; daily doses of antipsychotic are reported in this study as chlorpromazine equivalents. From an available sample of 110 patients with schizophrenia admitted to the Center during the recruitment period (January to April), 89 patients were considered suitable by the main researcher according to the information collected in retrospect from each patient's medical records, and were individually approached and screened for eligibility by their psychiatrist. Only 73 eligible patients consented to be included.

As healthy comparison subjects, we recruited 74 healthy individuals through advertising in the university campus and newspapers in the local community. These individuals were included if they were aged between 18 and 55 years and had no history of mental disorders, brain damage or drug use (at least in the last year) or addiction. Healthy comparison participants also had to score at or below the 50th percentile on all three dimensions of the Esquizo-Q questionnaire (Fonseca, Muñiz, Lemos & Villazón, 2010). This last inclusion criterion allowed us to exclude individuals with subclinical schizotypic traits. Based on the composition of the patient group, quotas for gender and age were set for the healthy comparison subjects group, and then an appropriate convenience sample of healthy comparison individuals was recruited.

Of the 73 patients who underwent testing, 9 were excluded because they did not complete the CPT (n = 4); because they failed to activate the button during testing, preventing any response data from being recorded (n = 2); or because they withdrew consent for their data to be used in the study after all testing had concluded (n = 3). Of the 74 recruited healthy comparison subjects, only 64 were included in the final analysis because they failed to activate the button during testing, preventing any response data from being recorded (n = 3); or they withdrew consent after testing had concluded (n = 7). None of the participants received any compensation for their involvement in the study.

Table 1 presents the basic characteristics of the patients and healthy comparison participants in this study.

Table 1.

Demographic and clinical characteristics of the participants

 Patients Mean (SDControl Mean (SD
Sex, % male 29.44 15.30 
Age, years 33.97 (9.38) 24.50 (6.86) 
Age at onset of illness 22.47 (6.83)  
Duration of illness, years 11.69 (8.68)  
Dose of antipsychotic, in chlorpromazine units 480.96 (515.73)  
PANSS   
 Positive 13.82 (5.78)  
 Negative 14.25 (6.27)  
Esquizo-Q   
 Distortion of reality  8.03 (3.55) 
 Negative dimension  11.83 (2.37) 
 Interpersonal disorganization  5.75 (0.74) 
 Patients Mean (SDControl Mean (SD
Sex, % male 29.44 15.30 
Age, years 33.97 (9.38) 24.50 (6.86) 
Age at onset of illness 22.47 (6.83)  
Duration of illness, years 11.69 (8.68)  
Dose of antipsychotic, in chlorpromazine units 480.96 (515.73)  
PANSS   
 Positive 13.82 (5.78)  
 Negative 14.25 (6.27)  
Esquizo-Q   
 Distortion of reality  8.03 (3.55) 
 Negative dimension  11.83 (2.37) 
 Interpersonal disorganization  5.75 (0.74) 

Note: PANSS, Positive and Negative Syndrome Scale.

Assessment and Instruments

The Positive and Negative Syndrome Scale (PANSS; Peralta & Cuesta, 1994) is a 30-item rating scale completed by a trained clinical researcher on the basis of chart review and a semi-structured interview. The present study used two of the five PANSS dimensions (Bell, Lysaker, Beam-Goulet, Milstein & Lindemayer, 1994), namely positive symptoms and negative symptoms.

The Oviedo Questionnaire for Assessing Schizotypy (ESQUIZO-Q, abbreviated version; Fonseca et al., 2010) is a self-report instrument for assessing healthy individuals for the presence of schizotypy. The abbreviated version comprises 23 items that respondents must answer using a Likert-type scale from 1 to 5. The items are distributed across three factors of the schizotypy dimension: distortion of reality, negative dimension, and interpersonal disorganization.

The CPT-II (Conners, 2004) asks participants to click a mouse button as quickly as possible each time a letter appears on the computer screen except the letter X, when they should instead inhibit their response. The target stimulus appears 90% of the time. The ISIs are 1, 2 or 4 s, and the display time is 250 msec. The entire test comprises 6 blocks of 60 trials each, for a total duration of 14 min. Prior to the test, participants perform a short practice test to become familiar with the process and to ensure that the task is understood.

We analyzed the raw scores of the 12 measures included in the standard CPT report (Table 2).

Table 2.

Measures analyzed in the standard CPT-II

Measure Definition Notes 
Omission errors Percentage of target letters to which the participant did not respond Assesses inability to maintain a repetitive motor action 
Commission errors Percentage of responses that occurred when the letter on the screen was not the target (letter XAssesses inability to inhibit a motor response and may indicate impulsive tendency 
Hit reaction time Mean response time (reaction time, in msec) for all target responses over all six trial blocks Assess response speed consistency. RT averaging over 900 ms is considered sluggish response 
Hit reaction time standard error Consistency of response time A high value indicates high variability in RTs, often related to inattentiveness 
Variability of standard error Represent variability in attention, or RT consistency, over time The amount of variability the individual shows in relation to his or her own overall standards error (“within respondent” variability) 
Detectability (d’) Measure of the difference between the signal (non-X) and noise (X) distribution This assesses sensorial performance independently of motivational aspects related to the response strategy. The greater the difference between the signal and noise distribution, the better the ability to distinguish and detect X and non-X stimuli 
Response style (β) The response criterion for the participant A strict criterion indicates a lower rate of commission errors and a higher rate of omission errors, while a lax criterion indicates the converse 
Perseverations Responses that occur less than 100 ms following a stimulus This allows detection of anticipatory or random responding, or frequent, very slow responses to the preceding stimuli 
Hit reaction time block change The slope of change in RT over the course of the test A positive slope indicates a slowing RT, while a negative slope indicates quicker RT as the test progresses 
Hit reaction time standard error block change The slope of change in consistency as the test progresses A positive slope reflects less consistency, indicating a possible loss of vigilance; a negative value indicates that RT becomes more consistent as the test progresses 
Hit reaction time ISI change The slope of change in RT over three ISIs (1, 2, and 4 s) A positive value indicates slower RTs as the time between targets increases; a negative value, faster RTs with longer time between targets 
Hit standard error ISI change The slope of change in RT standard errors over the three ISIs Positive slope indicates that the participant's RT becomes more erratic as the time between targets increases; negative slope means increased consistency as time between targets increases 
Measure Definition Notes 
Omission errors Percentage of target letters to which the participant did not respond Assesses inability to maintain a repetitive motor action 
Commission errors Percentage of responses that occurred when the letter on the screen was not the target (letter XAssesses inability to inhibit a motor response and may indicate impulsive tendency 
Hit reaction time Mean response time (reaction time, in msec) for all target responses over all six trial blocks Assess response speed consistency. RT averaging over 900 ms is considered sluggish response 
Hit reaction time standard error Consistency of response time A high value indicates high variability in RTs, often related to inattentiveness 
Variability of standard error Represent variability in attention, or RT consistency, over time The amount of variability the individual shows in relation to his or her own overall standards error (“within respondent” variability) 
Detectability (d’) Measure of the difference between the signal (non-X) and noise (X) distribution This assesses sensorial performance independently of motivational aspects related to the response strategy. The greater the difference between the signal and noise distribution, the better the ability to distinguish and detect X and non-X stimuli 
Response style (β) The response criterion for the participant A strict criterion indicates a lower rate of commission errors and a higher rate of omission errors, while a lax criterion indicates the converse 
Perseverations Responses that occur less than 100 ms following a stimulus This allows detection of anticipatory or random responding, or frequent, very slow responses to the preceding stimuli 
Hit reaction time block change The slope of change in RT over the course of the test A positive slope indicates a slowing RT, while a negative slope indicates quicker RT as the test progresses 
Hit reaction time standard error block change The slope of change in consistency as the test progresses A positive slope reflects less consistency, indicating a possible loss of vigilance; a negative value indicates that RT becomes more consistent as the test progresses 
Hit reaction time ISI change The slope of change in RT over three ISIs (1, 2, and 4 s) A positive value indicates slower RTs as the time between targets increases; a negative value, faster RTs with longer time between targets 
Hit standard error ISI change The slope of change in RT standard errors over the three ISIs Positive slope indicates that the participant's RT becomes more erratic as the time between targets increases; negative slope means increased consistency as time between targets increases 

Note: CPT, Continuous Performance Test; ISI, inter-stimulus interval.

Procedure

The study protocol was approved by the local ethics committee and all procedures conformed to international ethical norms, including the Declaration of Helsinki.

The testing procedure was identical for patients and healthy comparison subjects. The overall objectives of the study and the testing procedure were explained to participants individually. If they agreed to continue, then they were asked to sign an informed consent form and provide demographic and clinical data. Then, they completed the CPT. Afterwards patients were interviewed to allow the researchers to fill out the PANSS, while healthy subjects filled out the ESQUIZO-Q-A questionnaire. Assessments were done by the second author of the study after receiving specific relevant training.

The non-patients group contained university-educated people (30%) and people with no university education. The patient group contained 20% of individuals with university education. We were unable to include years of education as a variable in the analysis, because sufficiently reliable data could not be obtained for most participants. In addition, the years of study could not be imputed based on subjects’ age given that the number of years of obligatory education in [XXXX] has changed multiple times in recent decades.

Statistical Analysis

A cross-sectional design was used in order to allow analysis of the means between patients and healthy comparison participants. Data were analyzed using SPSS 19.0 (IBM, Chicago, IL). Inter-group differences in age were assessed for significance using Student's t test, while differences in gender distribution were assessed using the chi-squared test. Normal distribution of data was verified using the Kolmogorov–Smirnov test, after which differences in performance were assessed for significance using ANCOVA. In this analysis, sex and age served as covariates, following verification of the assumption of homogeneous regression slopes (Miller & Chapman, 2001). Percentiles were also analyzed in order to determine whether a participant showed normal or pathological performance for that variable according to the normative data included in the CPT manual. Pearson correlation was used to detect possible relationships between attentional performance and various dimensions of psychopathology in patients. In all analyses, results were calculated for a significance level of 0.05.

Results

ANCOVA of measured values was carried out to compare performance for patients and healthy comparison individuals on the CPT. Since the groups differed significantly in sex (z = −3.89, p < 0.05) and age (t = −6.52, p < 0.05), sex and age were covariates in the ANCOVA in order to control for the influence of these two variables. For all but two of the 12 measures, patients showed worse performance (Table 3). The two exceptions were Response Style and Hit Reaction Time ISI Change, which were similar between the groups. Figure 1 shows scatter plots of commission and omission errors, separately and together, for each of the two groups.

Fig. 1.

Scatter plots of commission and omission errors by patients and healthy comparison subjects.

Fig. 1.

Scatter plots of commission and omission errors by patients and healthy comparison subjects.

Table 3.

Differences in Conners’ CPT measures between patients with schizophrenia and healthy comparison subjects, as shown by analysis of covariance

CPT measure Patients Controls Fa p Partial η2 
Mean SD Mean SD 
Omission errors 4.02 5.61 0.61 1.72 12.51 0.001 0.092 
Commission errors 38.28 19.76 32.31 17.73 8.13 0.005 0.062 
Hit reaction time 447.47 94.35 356.87 55.94 22.19 0.000 0.152 
Hit reaction time standard error 10.16 5.20 5.17 1.57 41.26 0.000 0.25 
Variability of standard errors 18.14 15.05 6.52 3.40 29.37 0.000 0.191 
Detectability (d’0.75 0.44 0.84 0.44 4.01 0.048 0.031 
Response style (β) 1.30 1.90 0.62 0.69 2.03 0.157 0.016 
Perseverations 0.83 0.88 0.16 0.50 21.60 0.000 0.148 
Hit reaction time block change 0.01 0.04 −0.01 0.03 7.20 0.008 0.055 
Hit standard error block change 0.04 0.09 0.02 0.06 4.35 0.039 0.034 
Hit reaction time ISI change 0.06 0.05 0.06 0.03 2.64 0.106 0.021 
Hit standard error ISI change 0.04 0.15 0.01 0.09 5.59 0.020 0.043 
CPT measure Patients Controls Fa p Partial η2 
Mean SD Mean SD 
Omission errors 4.02 5.61 0.61 1.72 12.51 0.001 0.092 
Commission errors 38.28 19.76 32.31 17.73 8.13 0.005 0.062 
Hit reaction time 447.47 94.35 356.87 55.94 22.19 0.000 0.152 
Hit reaction time standard error 10.16 5.20 5.17 1.57 41.26 0.000 0.25 
Variability of standard errors 18.14 15.05 6.52 3.40 29.37 0.000 0.191 
Detectability (d’0.75 0.44 0.84 0.44 4.01 0.048 0.031 
Response style (β) 1.30 1.90 0.62 0.69 2.03 0.157 0.016 
Perseverations 0.83 0.88 0.16 0.50 21.60 0.000 0.148 
Hit reaction time block change 0.01 0.04 −0.01 0.03 7.20 0.008 0.055 
Hit standard error block change 0.04 0.09 0.02 0.06 4.35 0.039 0.034 
Hit reaction time ISI change 0.06 0.05 0.06 0.03 2.64 0.106 0.021 
Hit standard error ISI change 0.04 0.15 0.01 0.09 5.59 0.020 0.043 

Note: CPT, Continuous Performance Test; ISI, inter-stimulus interval. Significant differences are in bold (p < 0.05).

aF1,124.

The results for the 12 measures were distributed into percentiles to facilitate analysis of whether the results fell within the range of normal functioning. The recommendations and interpretations of the CPT manual were followed. Of the 10 measures on which the patients scored significantly worse than healthy subjects, patient's performance was within the range of normal functioning on four measures, slightly atypical on five, and moderately atypical on one (Table 4, Fig. 2).

Fig. 2.

Percentile performance of patients and healthy comparison patients. *Mildly atypical; **Moderately atypical.

Fig. 2.

Percentile performance of patients and healthy comparison patients. *Mildly atypical; **Moderately atypical.

Table 4.

Percentiles of Conners’ CPT measures

CPT measure Patients Controls 
Mean SD Mean SD 
Omission errors 73.42a 28.47 40.43 19.58 
Commission errors 54.52 29.40 50.79 29.36 
Hit reaction time 70.10a 28.48 32.72 25.51 
Hit reaction time standard error 86.06b 19.85 46.42 29.34 
Variability of standard errors 82.52a 21.89 40.99 28.14 
Detectability (d’53.78 26.94 51.73 26.83 
Response style (β) 55.18 24.56 43.91 17.31 
Perseverations 77.61a 26.75 47.35 17.53 
Hit reaction time block change 56.81 31.27 38.72 27.58 
Hit standard error block change 72.32a 26.24 62.17 25.49 
Hit reaction time ISI change 59.75 34.04 54.97 28.60 
Hit standard error ISI change 54.36 33.37 46.73 26.26 
CPT measure Patients Controls 
Mean SD Mean SD 
Omission errors 73.42a 28.47 40.43 19.58 
Commission errors 54.52 29.40 50.79 29.36 
Hit reaction time 70.10a 28.48 32.72 25.51 
Hit reaction time standard error 86.06b 19.85 46.42 29.34 
Variability of standard errors 82.52a 21.89 40.99 28.14 
Detectability (d’53.78 26.94 51.73 26.83 
Response style (β) 55.18 24.56 43.91 17.31 
Perseverations 77.61a 26.75 47.35 17.53 
Hit reaction time block change 56.81 31.27 38.72 27.58 
Hit standard error block change 72.32a 26.24 62.17 25.49 
Hit reaction time ISI change 59.75 34.04 54.97 28.60 
Hit standard error ISI change 54.36 33.37 46.73 26.26 

Note: CPT, Continuous Performance Test; ISI, inter-stimulus interval.

aMildly atypical.

bModerately typical.

To explore possible relationships between performance on the CPT and clinical characteristics of patients, we used Pearson's correlation to compare patient's performance on the 12 measures with age, age of illness onset, years of duration of illness, daily dose of antipsychotic medication (in g of chlorpromazine), and the two PANNS dimensions (Table 5). Because 72 correlations were tested, Bonferroni's correction was used to address the multiple comparisons problem (< 0.05/72). No significant correlations were found.

Table 5.

Pearson correlations between Conners’ CPT measures and demographic and clinical variables in patients with schizophrenia

CPT measure Age Age of onset of illness Duration of illness Dose of medicationa Positive symptoms Negative symptoms 
Omission errors 0.103 0.735 0.368 0.571 0.046 0.923 
Commission errors −0.176 −0.128 −0.042 0.172 0.117 0.124 
Hit reaction time 0.175 0.009 0.093 −0.011 0.020 −0.013 
Hit reaction time standard error −0.001 0.047 −0.054 0.045 0.087 −0.026 
Variability of standard errors −0.023 0.073 −0.079 0.047 0.043 −0.009 
Detectability (d’0.128 0.179 −0.042 −0.115 −0.211 −0.176 
Response style (β) 0.152 0.225 −0.100 −0.148 0.029 −0.137 
Perseverations −0.045 −0.034 0.016 0.097 −0.052 0.030 
Hit reaction time block change 0.037 −0.002 0.041 0.412 0.159 −0.077 
Hit standard error block change −0.129 −0.145 −0.062 0.297 0.161 0.136 
Hit reaction time ISI change −0.248 −0.030 −0.202 −0.109 −0.138 −0.113 
Hit standard error ISI change −0.265 0.120 −0.278 0.000 0.026 −0.077 
CPT measure Age Age of onset of illness Duration of illness Dose of medicationa Positive symptoms Negative symptoms 
Omission errors 0.103 0.735 0.368 0.571 0.046 0.923 
Commission errors −0.176 −0.128 −0.042 0.172 0.117 0.124 
Hit reaction time 0.175 0.009 0.093 −0.011 0.020 −0.013 
Hit reaction time standard error −0.001 0.047 −0.054 0.045 0.087 −0.026 
Variability of standard errors −0.023 0.073 −0.079 0.047 0.043 −0.009 
Detectability (d’0.128 0.179 −0.042 −0.115 −0.211 −0.176 
Response style (β) 0.152 0.225 −0.100 −0.148 0.029 −0.137 
Perseverations −0.045 −0.034 0.016 0.097 −0.052 0.030 
Hit reaction time block change 0.037 −0.002 0.041 0.412 0.159 −0.077 
Hit standard error block change −0.129 −0.145 −0.062 0.297 0.161 0.136 
Hit reaction time ISI change −0.248 −0.030 −0.202 −0.109 −0.138 −0.113 
Hit standard error ISI change −0.265 0.120 −0.278 0.000 0.026 −0.077 

Note: CPT, Continuous Performance Test; ISI, inter-stimulus interval.

aChlorpromazine equivalents.

Discussion

The aim of the present study was to analyze the performance of patients with schizophrenia on a CPT requiring a high response rate, in this case the standard Conners’ CPT-II. Patients performed significantly worse than healthy comparison subjects on all but 2 of the 12 measures analyzed, consistent with the idea that schizophrenia involves attentional deficits in a broad range of experimental tasks (Hahn et al., 2012; Hugdahl et al., 2013; Lysaker et al., 2010). A subject's performance on the CPT cannot be interpreted with reference to one overall measure but must be analyzed with reference to several dimensions of performance (Egeland & Kovalik-Gran, 2010). We have found significant differences in errors of omission between the two groups. This is consistent with a large number of works that have reported failures to sustain attention among people with schizophrenia assessed with CPT (see review by Nieto, 2016). By using a test requiring a high response rate, we hoped to be able to detect whether patients showed evidence of hyperactivity–impulsivity; we chose Conners’ CPT in part because it requires a high rate of responding and is widely used in the assessment of attention deficit hyperactivity disorder. We did, in fact, find significant differences in variables that measure impulsivity (commission errors, hit reaction time, and perseverations), suggesting that patients show a more impulsive response pattern than healthy participants. However, percentile analysis showed that patients’ rates of commission errors still fell within the normal range and, although patients’ RTs were slightly atypical, they were slow, not fast. This analysis suggests that even though CPTs may detect differences in hyperactivity–impulsivity between patients and healthy comparison subjects, the differences are unlikely to be clinically significant. Indeed, although our patients committed a significantly higher rate of commission errors than healthy subjects, they did not commit a significantly higher rate of omission errors or show RTs longer than 900 ms; these two criteria are typically used to conclude the existence of inattention (Egeland, 2007).

Our results suggest the existence of different patterns of attentional functioning in patients and non-patients, consistent with the factorial structure of the Conners’ CPT published by Egeland and Kovalik-Gran (2010). Those authors identified one factor, denominated “focus,” corresponding to the ability to concentrate attentional resources on a task while ignoring distracting stimuli. This attentional focus maybe a prerequisite for sustained attention and vigilance (Van der Meere, 2002) consistent with the hierarchical model of Sohlberg and Mateer (1989). Subjects with greater focus should commit omission errors more often and show greater variability in RTs for target (variability, Hit RT SE, perseverations). Egeland and Kovalik-Gran also identified the factor “hyperactivity–impulsivity,” a high level of which should correlate with a high rate of commission errors, fast RTs, and indiscriminate response style. Based on this factor structure, the percentile results in our study suggest that patients have problems focusing their attention, which can be observed as a low response rate on the CPT; their impulsivity, in contrast, falls within the normal range. These interpretations require further exploration of the factorial structure of Conners’ CPT.

Analysis of the response criterion (β) showed that both patients and healthy comparison subjects show the same response style: they tend to be liberal and risk taking when responding. That patients and healthy participants adopt a similar response style has been reported in studies that have explored this issue by analyzing performances (Birkett, Brindley, Norman, Harrison & Baddeley, 2006; Granholm, Asarnow & Marder, 1996; Harvey, Reichenberg, Romero, Granholm & Siever, 2006; Moriarty et al., 2003). This liberal tendency becomes stronger as the frequency of the target stimulus increases, at least in healthy individuals (Silverstein, Weinstein & Turnbull, 2004). Whether the same is true of patients with schizophrenia needs to be examined in future work.

Performance tests like CPT-II require the participant to inhibit an established motor response. Such inhibition may involve attentional control—a function of the executive system according to Baddeley's model—more than sustained attention (Posner & DiGirolamo, 1998). In this way, the CPT-II may be a better measure of learning or executive control of attention than a measure of the ability to maintain attention during a monotonous task. If so, performance on the CPT-II may be closely related to the integrity of frontal lobe function (Wu, Gau, Lo & Tseng, 2014). It would be interesting to perform neuroimaging studies to examine which zones are more active during this test.

In the first blocks of the test, participants must learn to establish a sufficiently fast response as the ISI changes, while at the same time inhibiting response during the appearance of non-target stimuli. Analysis of our data on Hit Reaction Time Standard Error and Variability of Standard Error indicates that patients showed greater RT variability and atypical functioning. These results are contrary to those of Egeland (2007), who concluded that the performance of patients with schizophrenia improved with time, in contrast to the performance of patients with attention deficit hyperactivity disorder or patients with depression (Egeland et al., 2003).

In summary, although patients with schizophrenia perform worse in most measures of CPT, their functioning is in some aspects within the normal range and so is not clinically significant. The performance in five measures was mildly atypical but the only significant pathological result was inconsistent in RTs, reflected in the index of variability. Our patients showed no evidence of clinically significant impulsivity or inattentiveness.

We chose to include sex and age as covariates in our analysis in order to control for any possible influence on CPT performance. Evidence suggests that neither variable, in fact, significantly affects attentional functioning on CPTs requiring low or high response frequency. Chan (2001) found no significant influence of sex, age, or educational level on the performance of patients with schizophrenia on the SART, a CPT requiring high response frequency. Giambra and Quilter (1988) found no association of age with either detection accuracy or time course on a vigilance task (Mackworth Clock-Test) in healthy people. Indeed, although age clearly influences sustained attention in infancy (Levy, 1980), it does not seem to affect sustained attention in younger or older adults (Parasuraman, Nestor & Greenwood, 1989).

Whether level of education can influence performance on CPT is unclear. Some studies suggest an association (Chen, Hsiao, Hsiao & Hwu, 1998), whereas others indicate no such association for CPTs requiring high response frequency (Chan, 2001) or low response frequency (Wu, Jiang & Gu, 2002). Unfortunately, we were unable to examine possible influence of years of education in our study for lack of reliable data. This is an important question for future research because several studies have provided strong evidence of an association between performance on the CPT and academic achievement (Campbell, D'Amato, Raggio & Stephens, 1991; Halperin, Sharma, Greenblatt & Schwartz, 1991).

We did not find a significant correlation between attentional deficits and clinical characteristics of schizophrenia. Using statistical correction to address the multiple comparisons makes it difficult to detect significances. Nevertheless, it is important to note the high association found between omission errors of the CPT and negative symptoms and age of illness onset. Sanz, Gómez, Vargas and Marín (2012) also reported correlation of negative symptomatology in patients with schizophrenia with their rate of omission errors, hit reaction time, and hit reaction time standard error on the CPT-II. The clinical significance of this correlation is unclear given that the patients showed quite mild symptomatology and data were not corrected for multiple testing. O'Grada and colleagues (2009) reported an association between negative symptomatology and index of variability in RTs on the SART (not-X CPT), while Chan and colleagues (2009) did not find a correlation between performance on SART and symptomatology scores on PANNS. Cornblatt, Lenzenweger, Dworkin and Erlenmeyer-Kimling (1985) associated negative symptoms with lowered processing capacity. Strauss, Buchanan and Hale (1993) found a relationship between CPT performance and thought disorder score on the BPRS, whereas several other studies reported no relationship between CPT and symptomatology (Addington & Addington, 1998; Kahn, Walker, Williams, Cornblatt & Mohs, 2012; Kurtz et al., 2001; Lysaker et al., 2010). The failure to find correlation is consistent with the idea that the deterioration of sustained attention in schizophrenia represents a core information processing deficit that is orthogonal to fluctuations in patient's symptoms, while studies that relate impairment in the CPT and negative symptoms argue that negative symptoms constitute relatively enduring trait-like characteristic in schizophrenia (Bozikas et al., 2005). These discrepant results may reflect the heterogeneity of CPTs (O'Grada et al., 2009), the diversity of CPT performance indicators (Liu et al., 1997), differences in symptomatology scales (Harvey and Keefe, 2001), or in sample composition (Kurtz et al., 2001). Future work should aim to elucidate in detail the heterogeneity of schizophrenia and to identify stable subtypes. Efforts to date have focused on combining cognitive tests and symptom scales, sometimes together with neuroimaging, but several studies have reported lack of correspondence between subtypes based on cognitive functioning and subtypes based on symptom profiles.

Although current drug therapy can be considered as a serious confounding factor that threatens the internal validity of a study, evidence suggests that such risk is minimal in the case of antipsychotic medications and CPT-like tests (Epstein, Keefe, Roitman, Harvey & Mohs, 1996; Krieger, Lis & Gallhofer, 2001). Indeed, both we in the present study using CPT-II and O'Grada and colleagues (2009) using SART failed to find an influence of daily chlorpromazine dose on performance.

Despite the insights provided by this study, its limitations should be kept in mind when interpreting the results. Since all the patients in our study were on medication, we could not perform subgroup analysis to examine whether medicated and non-medicated patients differ significantly in CPT-II performance. Our patients did not, on average, have serious symptomatology, and some of them presented similar scores for positive and negative symptoms. It would be interesting to repeat our tests on patients with more severe symptoms or patients with primarily positive or negative symptoms. Lastly, we looked at a limited number of variables and failed to identify patients showing clinically significant impulsive behavior.

We were unable to examine possible confounding effects of nicotine on CTP performance in our study, for lack of reliable data about smoking behavior. This is an important factor to take into account, given that rates of tobacco use are higher among patients with schizophrenia than in the general population (Smith et al., 2006; D'Souza & Markou, 2012). Nevertheless, meta-analysis of the effects of nicotine on cognitive performance has not provided a clear picture (Heishman, Kleykamp & Singleton, 2010; Sacco, Bannon & George, 2004). One study found no effect of tobacco on attentional performance of patients with schizophrenia on Conners’ CPT (Morisano, Wing, Sacco, Arenovich & George, 2013); another study found no difference between patients who quit smoking and those who did not (Dolan et al., 2004), leading the authors to conclude that sustained attention is not associated with response to smoking cessation treatment. Roth, Hong, McMahon and Fuller (2013) found that the CPT-IP was more sensitive than Conners’ CPT for differentiating smoker and non-smoker patients. This result, together with those of several other studies, suggests that nicotine may influence cognitive performance under highly specific circumstances (Morisano et al., 2013), highlighting the need for including it in future work.

Conflict of Interest

None declared.

References

Aaron
,
P. G.
,
Joshi
,
R. M.
, &
Phipps
,
J.
(
2004
).
A cognitive tool to diagnose predominantly inattentive ADHD behavior
.
Journal of Attention Disorders
 ,
7
,
125
135
.
Addington
,
J.
, &
Addington
,
D.
(
1998
).
Visual attention and symptoms in schizophrenia: A 1-year follow-up
.
Schizophrenia Research
 ,
34
,
95
99
.
American Psychiatric Association
(
2013
).
Diagnostic and Statistical Manual of Mental Disorders. Fifth Edition. DSM-5
 .
Arlington, VA
:
American Psychiatric Publishing
.
Ballard
,
J.
(
1996
).
Computerized assessment of sustained attention: a review of factors affecting vigilance performance
.
Journal of Clinical and Experimental Neuropsychology
 ,
18
,
843
863
.
Barch
,
D. M.
(
2005
).
The cognitive neuroscience of schizophrenia
.
Annual Review of Clinical Psychology
 ,
1
,
321
353
.
Bell
,
M. D.
,
Lysaker
,
P. H.
,
Beam-Goulet
,
J. L.
,
Milstein
,
R. M.
, &
Lindemayer
,
J. P.
(
1994
).
Five-component model of schizophrenia: Assessing the factorial invariance of the positive and negative syndrome scale
.
Psychiatry Research
 ,
52
,
295
303
.
Birkett
,
P.
,
Brindley
,
A.
,
Norman
,
P.
,
Harrison
,
G.
, &
Baddeley
,
A.
(
2006
).
Control of attention in schizophrenia
.
Psychiatry Research
 ,
40
,
579
588
.
Bozikas
,
P. V.
,
Andreou
,
C.
,
Giannakou
,
M.
,
Tonia
,
T.
,
Anezoulaki
,
D.
,
Karavatos
,
A.
, et al
. (
2005
).
Deficits in sustained attention in schizophrenia but not in bipolar disorder
.
Schizophrenia Research
 ,
78
,
225
233
.
Buchanan
,
R. W.
,
Strauss
,
M. E.
,
Brier
,
A.
,
Kirkpatrick
,
B.
, &
Carpenter
,
W. T.
(
1997
).
Attentional impairment in deficit and non-deficit forms of schizophrenia
.
American Journal of Psychiatry
 ,
154
,
363
370
.
Campbell
,
J. W.
,
D'Amato
,
R. C.
,
Raggio
,
D. J.
, &
Stephens
,
K. D.
(
1991
).
Construct validity of the computerized Continuous Performance Test with measures of intelligence, achievement and behavior
.
Journal of School Psychology
 ,
29
,
143
150
.
Chan
,
R. C. K.
(
2001
).
A further study on the sustained attention response to task (SART): The effect of age, gender and education
.
Brain Injury
 ,
15
(9)
,
819
829
.
Chan
,
R. C. K.
,
Wang
,
Y.
,
Cheung
,
E. F. C.
,
Cui
,
J.
,
Deng
,
Y.
,
Yuan
,
Y.
, et al
. (
2009
).
Sustained attention deficit along the psychosis proneness continuum. A study on the Sustained Attention to Response Task (SART)
.
Cognitive and Behavioral Neurology
 ,
22
(3)
,
180
185
.
Chen
,
W. J.
,
Hsiao
,
C. K.
,
Hsiao
,
L. L.
, &
Hwu
,
H. G.
(
1998
).
Performance of the Continuous Performance Test among community samples
.
Schizophrenia Bulletin
 ,
24
,
163
174
.
Cheyne
,
J. A.
,
Carriere
,
J. S. A.
, &
Smilek
,
D.
(
2006
).
Absent-mindedness: Lapses of conscious awareness and everyday cognitive failures
.
Consciousness and Cognition
 ,
15
,
578
592
.
Cohen
,
A. S.
,
Saperstein
,
A. M.
,
Gold
,
J. M.
,
Kirkpatrick
,
B.
,
Carpenter
,
W. T.
, &
Buchanan
,
R. W.
(
2007
).
Neuropsychology of the deficit syndrome: New data and meta-analysis of findings to date
.
Schizophrenia Bulletin
 ,
33
,
1201
1212
.
Conners
,
C. K.
(
2004
).
Conners’ Continuous Performance Test (CPT-II). Technical Guide and Software Manual
 .
Canada
:
Multi Health System
.
Cornblatt
,
B. A.
, &
Malhotra
,
K. A.
(
2001
).
Impaired attention as an endophenotype for molecular genetic studies of schizophrenia
.
American Journal of Medical Genetics
 ,
105
,
11
15
.
Cornblatt
,
B. A.
,
Lenzenweger
,
M. F.
,
Dworkin
,
R. H.
, &
Erlenmeyer-Kimling
,
L.
(
1985
).
Positive and negative schizophrenic symptoms attention and information processing
.
Schizophrenia Bulletin
 ,
11
,
397
408
.
Cornblatt
,
B. A.
,
Lenzenweger
,
M. F.
, &
Erlenmeyer-Kimling
,
L.
(
1989
).
The Continuous Performance Test, Identical Pairs Version: II. Contrasting attentional profiles in schizophrenic and depressed patients
.
Psychiatry Research
 ,
29
,
65
85
.
Cornblatt
,
B. A.
,
Obuchowski
,
M.
,
Schnur
,
B.
, &
O'Brien
,
J. D.
(
1997
).
Attention and clinical symptoms in schizophrenia
.
Psychiatric Quarterly
 ,
68
,
343
359
.
Dolan
,
S. L.
,
Sacco
,
K. A.
,
Termine
,
A.
,
Seval
,
A. A.
,
Dudas
,
M. M.
,
Vessicchio
,
J. C.
, et al
. (
2004
).
Neuropsychological deficits are associated with smoking cessation treatment failure in patients with schizophrenia
.
Schizophrenia Research
 ,
70
,
263
275
.
D'Souza
,
M. S.
, &
Markou
,
A.
(
2012
).
Schizophrenia and tobacco smoking comorbidity: nAChR agonist in the treatment of schizophrenia associated cognitive deficits
.
Neuropharmacology
 ,
623
,
1564
1573
.
Egeland
,
J.
(
2007
).
Differentiating attention deficit in adult ADHD and schizophrenia
.
Archives of Clinical Neuropsychology
 ,
22
,
763
771
.
Egeland
,
J.
, &
Kovalik-Gran
,
I.
(
2010
).
Measuring several aspects of attention in one test. The factor structure of Conners's Continuous Performance Test
.
Journal of Attention Disorders
 ,
13
,
339
346
.
Egeland
,
J.
,
Rund
,
B. R.
,
Sundet
,
K.
,
Landrø
,
N. I.
,
Asbjørnsen
,
A.
,
Lund
,
A.
, et al
. (
2003
).
Attention profile in schizophrenia compared to depression: Differential effects of processing speed, selective attention and vigilance
.
Acta Psychiatrica Scandinavica
 ,
108
,
276
284
.
Epstein
,
J. I.
,
Keefe
,
R. S. E.
,
Roitman
,
S. L.
,
Harvey
,
P. D.
, &
Mohs
,
R. C.
(
1996
).
Impact of neuroleptic medications on Continuous Performance Test measures in schizophrenia
.
Biological Psychiatry
 ,
39
,
902
905
.
Fear
,
C.
,
Sharp
,
H.
, &
Healy
,
D.
(
1996
).
Cognitive processes in delusional disorders
.
British Journal of Psychiatry
 ,
168
,
61
67
.
Fonseca
,
J.
,
Muñiz
,
J.
,
Lemos
,
S.
, &
Villazón
,
U.
(
2010
).
The Oviedo Questionnaire for Assessing Schizotypy
 .
Madrid, Spain
:
TEA Ediciones
.
Giambra
,
L. M.
, &
Quilter
,
R. E.
(
1988
).
Sustained attention in adulthood: a unique, large-sample, longitudinal and multicohort analysis using the Mackworth Clock-Test
.
Psychology and Aging
 ,
1
,
75
83
.
Granholm
,
E.
,
Asarnow
,
R. F.
, &
Marder
,
S. R.
(
1996
).
Dual-task performance operating characteristics, resource limitations, and automatic processing in schizophrenia
.
Neuropsychology
 ,
10
(1)
,
11
21
.
Grawe
,
R. W.
, &
Levander
,
S.
(
2001
).
Neuropsychological impairments in patients with schizophrenia: stability and prediction of outcome
.
Acta Psychiatrica Scandinavica
 ,
104
,
60
64
.
Green
,
D. M.
, &
Swets
,
J. A.
(
1966
).
Signal Detection Theory and Psychophysics
 .
New York
:
Willey
.
Hahn
,
B.
,
Robinson
,
B. M.
,
Harvey
,
A. N.
,
Kaiser
,
S. T.
,
Leonard
,
C. J.
,
Luck
,
S. J.
, et al
. (
2012
).
Visuospatial attention in schizophrenia: Deficits in broad monitoring
.
Journal of Abnormal Psychology
 ,
121
(1)
,
119
128
.
Halperin
,
J. M.
,
Sharma
,
V.
,
Greenblatt
,
E.
, &
Schwartz
,
S. T.
(
1991
).
Assessment of the Continuous Performance Test: Reliability and validity in a nonreferred sample
.
Psychological Assessment
 ,
3
,
603
608
.
Harrison
,
P. J.
, &
Weinberger
,
D. R.
(
2005
).
Schizophrenia genes, gene expression, and neuropathology: on the matter of their convergence
.
Molecular Psychiatry
 ,
10
,
40
68
.
Harvey
,
P. D.
, &
Keefe
,
R. S.
(
2001
).
Studies of cognitive change in patients with schizophrenia following novel antipsychotic treatment
.
The American Journal of Psychiatry
 ,
158
(2)
,
176
184
.
Harvey
,
P. D.
,
Rabinowitz
,
J.
,
Eerdekens
,
M.
, &
Davidson
,
M.
(
2005
).
Treatment of cognitive impairment in early psychosis: A comparison of risperidone and haloperidol in a large long-term trial
.
American Journal of Psychiatry
 ,
162
,
1888
1895
.
Harvey
,
P. D.
,
Reichenberg
,
A.
,
Romero
,
M.
,
Granholm
,
E.
, &
Siever
,
L. J.
(
2006
).
Dual-task information processing in schizotypal personality disorder: evidence of impaired processing capacity
.
Neuropsychology
 ,
20
(4)
,
453
460
.
Hazlett
,
E. A.
,
Dawson
,
M. E.
,
Schell
,
A. M.
, &
Nuechterlein
,
K. H.
(
2008
).
Probing attentional dysfunctions in schizophrenia: Startle modification during a continuous performance test
.
Psychophysiology
 ,
45
,
632
642
.
Heinrichs
,
R. W.
(
2005
).
The primacy of cognition in schizophrenia
.
American Psychologist
 ,
60
,
229
242
.
Heinrichs
,
R. W.
, &
Zakzanis
,
K. K.
(
1998
).
Neurocognitive deficits in schizophrenia: a quantitative review of the evidence
.
Neuropsychology
 ,
12
,
426
445
.
Heishman
,
S. J.
,
Kleykamp
,
B. A.
, &
Singleton
,
E. G.
(
2010
).
Meta‐analysis of the acute effects of nicotine and smoking on human performance
.
Psychopharmacology
 ,
210
,
453
469
.
Honey
,
G. D.
,
Sharma
,
T.
,
Suckling
,
J.
,
Giampietro
,
V.
,
Soni
,
W.
,
Williams
,
S. C.
, et al
. (
2003
).
The functional neuroanatomy of schizophrenic subsyndromes
.
Psychological Medicine
 ,
33
,
1007
1018
.
Hugdahl
,
K.
,
Nygård
,
M.
,
Falkenberg
,
L. E.
,
Kompus
,
K.
,
Westerhausen
,
R.
,
Kroken
,
R.
, et al
. (
2013
).
Failure of attention focus and cognitive control in schizophrenia patients with auditory verbal hallucinations: Evidence from dichotic listening
.
Schizophrenia Research
 ,
147
(2–3)
,
301
309
.
Ikebuchi
,
E.
,
Nakagome
,
K.
, &
Takahashi
,
N.
(
1999
).
How do early stages of information processing influence social skills in patients with schizophrenia
.
Schizophrenia Research
 ,
35
,
255
262
.
Kahn
,
P. V.
,
Walker
,
T. M.
,
Williams
,
T. S.
,
Cornblatt
,
B. A.
, &
Mohs
,
R. C.
(
2012
).
Standardizing the use of the Continuous Performance Test in schizophrenia research: A validation study
.
Schizophrenia Research
 ,
142
(1–3)
,
153
158
.
Kalkstein
,
S.
,
Hurford
,
I.
, &
Gur
,
R. C.
(
2010
).
Neurocognition in schizophrenia
.
Current Topic in Behavioral Neurosciences
 ,
4
,
373
390
.
Keefe
,
R. S.
,
Perkins
,
D. O.
,
Gu
,
H.
,
Zipursky
,
R. B.
,
Christensen
,
B. K.
, &
Lieberman
,
J. A.
(
2006
).
A longitudinal study of neurocognitive function in individuals at-risk for psychosis
.
Schizophrenia Research
 ,
88
,
26
35
.
Keshavan
,
M. S.
,
Tandon
,
R.
,
Boutros
,
N. N.
, &
Nasrallah
,
H. A.
(
2008
).
Schizophrenia, “just the facts”: what we know in 2008: Part 3: neurobiology
.
Schizophrenia Research
 ,
106
,
89
107
.
Krieger
,
S.
,
Lis
,
S.
, &
Gallhofer
,
B.
(
2001
).
Cognitive subprocesses and schizophrenia. A reaction-time decomposition
.
Acta Psychiatrica Scandinavica Supplementum
 ,
408
,
18
27
.
Kumar
,
C. T.
,
Christodoulou
,
T.
,
Vyas
,
N. S.
,
Kyriakopoulos
,
M.
,
Corrigall
,
R.
,
Reichenberg
,
A.
, et al
. (
2010
).
Deficits in visual sustained attention differentiate genetic liability and disease expression for schizophrenia from bipolar disorder
.
Schizophrenia Research
 ,
124
(1–3)
,
152
60
.
Kurtz
,
M. M.
,
Ragland
,
J. D.
,
Bilker
,
W.
,
Gur
,
R. C.
, &
Gur
,
R. E.
(
2001
).
Comparison of the continuous performance test with and without working memory demands in healthy controls and patients with schizophrenia
.
Schizophrenia Research
 ,
48
(2-3)
,
307
316
.
Lee
,
K. H.
,
Tsoi
,
D. T.
,
Khokhar
,
W. A.
,
Swalli
,
J. S.
,
Gee
,
K.
,
Pluck
,
G.
, et al
. (
2012
).
Performance on the continuous performance test under parametric increase of working memory load in schizophrenia
.
Psychiatry Research
 ,
197
,
350
352
.
Lesh
,
T. A.
,
Niendam
,
T. A.
,
Minzenberg
,
M. J.
, &
Carter
,
C. S.
(
2011
).
Cognitive control deficits in schizophrenia: Mechanisms and meaning
.
Neuropsychopharmacology
 ,
36
,
316
338
.
Levy
,
F.
(
1980
).
The development of sustained attention (vigilance) and inhibition in children: Some normative data
.
Journal of Child Psychology and Psychiatry
 ,
21
,
72
84
.
Liddle
,
P. F.
(
2000
).
Cognitive impairment in schizophrenia: Its impact on social functioning
.
Acta Psychiatrica Scandinavica
 ,
101
,
11
16
.
Liu
,
S. K.
,
Hwu
,
H. G.
, &
Chen
,
W. J.
(
1997
).
Clinical symptom dimensions and deficits on the Continuous Performance Test in schizophrenia
.
Schziophrenia Research
 ,
25
,
211
219
.
Liu
,
S. K.
,
Hsieh
,
M. H.
,
Hwang
,
T. J.
,
Hwu
,
H. G.
,
Liao
,
S. C.
,
Lin
,
S. H.
, et al
. (
2006
).
Re-examining sustained attention deficits as vulnerability indicators for schizophrenia: Stability in the long term course
.
Journal of Psychiatric Research
 ,
40
,
613
621
.
Lysaker
,
P. H.
,
Tsai
,
J.
,
Henninger
,
L. L.
,
Vohs
,
J. L.
, &
Viverito
,
K.
(
2010
).
Decrements in sustained attention across trials in a Continuous Performance Test. Associations with social functioning in schizophrenia
.
The Journal of Nervous and Mental Disease
 ,
198
,
154
158
.
Manly
,
T.
,
Robertson
,
I. H.
,
Galloway
,
M.
, &
Hawkins
,
K.
(
1999
).
The absent mind: Further investigations of sustained attention to response
.
Neuropsychologia
 ,
37
,
661
670
.
Mass
,
R.
(
2002
).
The vigilance paradigm in schizophrenia research - studies on the Continuous Performance Test (CPT)
.
Fortschritte der Neurologie-Psychiatrie
 ,
70
(1)
,
34
9
.
Miller
,
G. A.
, &
Chapman
,
J. P.
(
2001
).
Misunderstanding analysis of covariance
.
Journal of Abnormal Psychology
 ,
110
,
40
48
.
Mirsky
,
A. F.
,
Anthony
,
B. J.
,
Duncan
,
C. C.
,
Ahearn
,
M. B.
, &
Kellam
,
S. G.
(
1991
).
Analysis of elements of attention: A neuropsychological approach
.
Neuropsychology Review
 ,
2
,
109
145
.
Moriarty
,
P. J.
,
Harvey
,
P. D.
,
Mitropoulou
,
V.
,
Granholm
,
E.
,
Silverman
,
J. M.
, &
Siever
,
L. J.
(
2003
).
Reduced processing resource availability in schizotypal personality disorder: evidence from a dual-task CPT study
.
Journal of Clinical and Experimental Neuropsychology
 ,
25
(3)
,
335
347
.
Morisano
,
D.
,
Wing
,
V. C.
,
Sacco
,
K. A.
,
Arenovich
,
T.
, &
George
,
T. P.
(
2013
).
Effects of tobacco smoking on neuropsychological function in schizophrenia in comparison to other psychiatric disorders and non‐psychiatric controls
.
The American Journal on Addictions
 ,
22
,
46
53
.
Nieto
,
M.
(
2016
). La atención sostenida como marcador de vulnerabilidad de la esquizofrenia: una serie de meta-análisis de estudios con Test de Ejecución Continua (CPT). [Sustained attention as a vulnerability marker for schizophrenia: a series of meta-analysis on Continuous Performance Test (CPT) studies]. Doctoral dissertation,
Madrid, Spain
,
Universidad Complutense de Madrid
.
Nieuwenstein
,
M. R.
,
Aleman
,
A.
, &
de Haan
,
E. H. F.
(
2001
).
Relationship between symptom dimensions and neurocognitive functioning in schizophrenia: a meta-analysis of WCST and CPT studies
.
Journal of Psychiatry Research
 ,
35
,
119
125
.
Nuechterlein
,
K. H.
,
Dawson
,
M. E.
, &
Green
,
M. F.
(
1994
).
Information-processing abnormalities as neuropsychological vulnerability indicators for schizophrenia
.
Acta Psychiatrica Scandinavica
 ,
90
,
71
79
.
Nuechterlein
,
K. H.
,
Green
,
M. F.
,
Calkins
,
M. E.
,
Greenwood
,
T. A.
,
Gur
,
R. E.
,
Gur
,
R. C.
, et al
. (
2015
).
Attention/vigilance in schizophrenia: Performance results from a large multi-site study of the Consortium on the Genetics of Schizophrenia (COGS)
.
Schizophrenia Research
 ,
163
,
38
46
.
Oberauer
,
K.
(
2002
).
Access to information in working memory: exploring the focus of attention
.
Journal of Experimental Psychology: Learning, Memory, and Cognition
 ,
28
,
411
421
.
O'Grada
,
C.
,
Barry
,
S.
,
McGlade
,
N.
,
Behan
,
C.
,
Haq
,
F.
,
Hayden
,
J.
, et al
. (
2009
).
Does the ability to sustain attention underlie symptom severity in schizophrenia
.
Schizophrenia Research
 ,
107
,
319
323
.
Olsen
,
A.
,
Ferenc-Brunner
,
J.
,
Evensen
,
K. A.
,
Garzon
,
B.
,
Landrø
,
N. I.
, &
Håberg
,
A. K.
(
2013
).
The functional topography and temporal dynamics of overlapping and distinct brain activations for adaptive task control and stable task-set maintenance during performance of an fMRI-adapted clinical continuous performance test
.
Journal of Cognitive Neuroscience
 ,
25
,
903
19
.
Parasuraman
,
R.
,
Nestor
,
P.
, &
Greenwood
,
P.
(
1989
).
Sustained-attention capacity in young and older adults
.
Psychology and Aging
 ,
4
(3)
,
339
345
.
Penadés
,
R.
,
Gastó
,
C.
,
Boget
,
T.
,
Catalán
,
R.
, &
Salamero
,
M.
(
2001
).
Deficit in schizophrenia: the relationship between negative symptoms and neurocognition
.
Comprehensive Psychiatry
 ,
42
,
64
69
.
Peralta
,
V.
, &
Cuesta
,
M. L.
(
1994
).
Validation of positive and negative symptom scale (PANSS) in a sample of Spanish schizophrenic patients
.
Actas Luso-Españolas de Neurología, Psiquiatría y Ciencias Afines
 ,
22
,
171
177
.
Posner
,
M. I.
, &
DiGirolamo
,
G. J. U.
(
1998
). Executive attention: Conflict, target detection and cognitive control. In
Parasuraman
R.
(Ed.)
The Attention Brain
  (pp.
401
423
).
Cambridge
:
The MIT Press
.
Pukrop
,
R.
,
Ruhrmann
,
S.
,
Schultze-Lutter
,
F.
,
Bechdolf
,
A.
,
Brockhaus-Dumke
,
A.
, &
Klosterkötter
,
J.
(
2007
).
Neurocognitive indicators for a conversion to psychosis: Comparison of patients in a potentially initial prodromal state who did or did not convert to a psychosis
.
Schizophrenia Research
 ,
92
,
119
125
.
Rapisarda
,
A.
,
Kraus
,
M.
,
Tan
,
Y. W.
,
Lam
,
M.
,
Eng
,
G. K.
,
Lee
,
J.
, et al
. (
2014
).
The continuous performance test, identical pairs, norms, reliability and performance in healthy controls and patients with schizophrenia on Singapore
.
Schizophrenia Research
 ,
156
,
233
240
.
Ren
,
W.
,
Lui
,
S.
,
Deng
,
W.
,
Li
,
F.
,
Li
,
M.
,
Huang
,
X.
, et al
. (
2013
).
Anatomical and functional brain abnormalities in drug-naïve first-episode schizophrenia
.
American Journal of Psychiatry
 ,
170
,
1308
1316
.
Riccio
,
C. A.
,
Reynolds
,
C. R.
, &
Lowe
,
P. A.
(
2001
).
Clinical Applications of Continuous Performance Test.
 .
Canada
:
John Wiley and Sons
.
Robertson
,
I. H.
,
Manly
,
T.
,
Andrade
,
J.
,
Baddeley
,
B. T.
, &
Yiend
,
J.
(
1997
).
“Oops!” Performance correlates of everyday attentional failures in traumatic brain injured and normal subjects
.
Neuropsychologia
 ,
35
,
747
758
.
Rosvold
,
H. E.
,
Mirsky
,
A.
,
Sarason
,
I.
,
Bransome
,
E. D.
, &
Beck
,
L. H.
(
1956
).
A Continuous Performance Test of brain damage
.
Journal of Consulting Psychology
 ,
20
,
343
350
.
Roth
,
M.
,
Hong
,
L. E.
,
McMahon
,
R. P.
, &
Fuller
,
R. L.
(
2013
).
Comparison of the effectiveness of Conners’ CPT and the CPT-identical pairs at distinguishing between smokers and nonsmokers with schizophrenia
.
Schizophrenia Research
 ,
148
,
29
33
.
Rund
,
B. R.
,
Melle
,
I.
,
Friis
,
S.
,
Larsen
,
T. K.
,
Midbøe
,
L. J.
,
Opjordsmoen
,
S.
, et al
. (
2004
).
Neurocognitive dysfunctions in first episode psychosis: Correlates with symptoms premorbid adjustment and duration of untreated psychosis
.
American Journal of Psychiatry
 ,
161
,
466
472
.
Rund
,
B. R.
,
Sundet
,
K.
,
Asbjørnsen
,
A.
,
Egeland
,
J.
,
Landrø
,
N. I.
,
Lund
,
A.
, et al
. (
2006
).
Neuropsychological test profiles in schizophrenia and non-psychotic depression
.
Acta Psychiatrica Scandinavica
 ,
113
,
350
359
.
Sacco
,
K. A.
,
Bannon
,
K. L.
, &
George
,
T. P.
(
2004
).
Nicotinic receptor mechanisms and cognition in normal states and neuropsychiatric disorders
.
Journal of Psychopharmacology
 ,
18
,
457
474
.
Sanz
,
J. C.
,
Gómez
,
V.
,
Vargas
,
M. L.
, &
Marín
,
J. J.
(
2012
).
Dimensions of attention impairment and negative symptoms in schizophrenia: a multidimensional approach using the Conners Continuous Performance Test in a Spanish Population
.
Cognitive and Behavioral Neurology
 ,
25
,
63
71
.
Seltzer
,
J.
,
Conrad
,
C.
, &
Cassens
,
G.
(
1997
).
Neuropsychological profiles in schizophrenia: paranoid versus undifferentiated distinctions
.
Schizophrenia Research
 ,
23
,
131
138
.
Silverstein
,
M. L.
,
Weinstein
,
M.
, &
Turnbull
,
A.
(
2004
).
Nonpatient CPT performance varying target frequency and interstimulus interval on five response measures
.
Archives of Clinical Neuropsychology
 ,
19
,
1017
1025
.
Smith
,
R. C.
,
Warner-Cohen
,
J.
,
Matute
,
M.
,
Butler
,
E.
,
Kelly
,
E.
,
Vaidhyanathaswamy
,
S.
, et al
. (
2006
).
Effects of nicotine nasal spray on cognitive function in schizophrenia
.
Neuropsychopharmacology
 ,
31
,
637
643
.
Snitz
,
B. E.
,
MacDonald
,
A. W.
, &
Carter
,
C. S.
(
2006
).
Cognitive deficits in unaffected first-degree relatives of schizophrenia patients: A meta-analytic review of putative endophenotypes
.
Schizophrenia Bulletin
 ,
32
(1)
,
179
194
.
Sohlberg
,
M. M.
, &
Mateer
,
C. A.
(
1989
).
Training use of compensator memory books: a three stage behavioural approach
.
Journal of Clinical and Experimental Neuropsychology
 ,
11
,
891
971
.
Strauss
,
M. E.
,
Buchanan
,
R. W.
, &
Hale
,
J.
(
1993
).
Relations between attentional deficits and clinical symptoms in schizophrenic outpatients
.
Psychiatry Research
 ,
47
,
205
213
.
Van der Meere
,
J. J.
(
2002
). The role of attention. In
Sandberg
(Ed.)
Hyperactivity and Attention Disorders of Childhood
 .
Cambridge, UK
:
Cambridge University Press
.
Vázquez
,
C.
,
Nieto-Moreno
,
M.
,
Cerviño
,
M. J.
, &
Fuentenebro
,
F.
(
2006
).
Effects of increasing cognitive load on sustained attention tasks in schizophrenic disorders and schizotypy
.
Psicothema
 ,
18
,
221
227
.
Villalta-Gil
,
V.
,
Vilaplana
,
M.
,
Ochoa
,
S.
,
Haro
,
J. M.
,
Dolz
,
M.
,
Usall
,
J.
, et al
. (
2006
).
Neurocognitive performance and negative symptoms: Are they equal in explaining disability in schizophrenia outpatients
.
Schizophrenia Research
 ,
87
,
246
253
.
Voruganti
,
L. N.
,
Heslegrave
,
R. J.
, &
Awad
,
A. G.
(
1997
).
Neurocognitive correlates of positive and negative syndromes in schizophrenia
.
Canadian Journal of Psychiatry
 ,
42
,
1066
1071
.
Waters
,
F. A.
,
Badcock
,
J. C.
,
Michie
,
P. T.
, &
Maybery
,
M. T.
(
2006
).
Auditory hallucinations in schizophrenia: Intrusive thoughts and forgotten memories
.
Cognitive Neuropsychiatry
 ,
11
,
65
83
.
Wu
,
T.
,
Jiang
,
C.
, &
Gu
,
X.
(
2002
).
Continuous performance test in 77 normal adults
.
Chinese Mental Health Journal
 ,
16
,
158
159
.
Wu
,
Y. H.
,
Gau
,
S. S.
,
Lo
,
Y. C.
, &
Tseng
,
W. Y.
(
2014
).
White matter tract integrity of frontostriatal circuit in attention deficit hyperactivity disorder: association with attention performance and symptoms
.
Human Brain Mapping
 ,
35
,
199
212
.
Yung
,
A. R.
,
Phillips
,
L. J.
,
Yuen
,
H. P.
, &
McGorry
,
P. D.
(
2004
).
Risk factors for psychosis in an ultra high-risk group: Psychopathology and clinical features
.
Schizophrenia Research
 ,
67
,
131
470
.
Yung
,
A. R.
,
Yuen
,
H. P.
,
Berger
,
G.
,
Francey
,
S.
,
Hung
,
T. C.
,
Nelson
,
B.
, et al
. (
2007
).
Declining transition rate in ultra high risk (prodromal) services: dilution or reduction of risk
.
Schizophrenia Bulletin
 ,
33
,
673
681
.